Methodological Issues in Measuring Alcohol Use

Various methodological issues influence the measurement of alcohol consumption in surveys. One factor is the reference period for which questions are asked—that is, whether respondents are asked for an exact recall of their intake during a short, recent period or for a summary of their drinking behavior over a longer period, such as the past year. Longer recall periods provide sufficient time to link consumption data with concurrently collected data on the prevalence of alcohol-related outcomes. Another factor influencing survey results is the approach used to measure alcohol consumption. Two commonly used measures are the usual quantity/frequency (QF) and graduated frequency (GF) approaches, both of which allow researchers to estimate the volume of alcohol intake. Other issues that researchers conducting surveys should consider include the use of beverage-specific versus overall questions, open-ended versus categorical responses, and measurement of standard versus actual drink sizes. Finally, features of the overall survey design—such as the mode of interview (i.e., in person versus by telephone), the use of computerized survey instruments, and measures to ensure confidentiality—influence the reliability and validity of the data.

O ne important goal of alcohol epidemiology is to link alco hol consumption with alcohol-related problems. To this end, alcohol consumption first must be determined as accurately as possible. At the level of a large population, aggregate-level analyses, such as those that compare variation in per capita alcohol consumption and mortality rates over time, are useful in demon strating links between consumption and its sequelae. Consumption data for such aggregate analyses typically are based on information about alco hol sales or shipments. At least in the United States, these data represent the standard against which other esti mates of alcohol consumption are compared.
In contrast, analyses that link drinking behavior with related outcomes at the individual level generally rely on survey data. Surveys of con sumption allow researchers to ask individuals about their drinking patterns and to obtain other potentially related information, such as socio demographic characteristics, health status, and alcohol-related experi ences. Most important, this approach enables investigators to link alcohol consumption with various outcomes at the level of the individual respon dent as well as to adjust for other individual characteristics that might confound the associations being stud ied. In addition, survey data permit researchers to identify abstainers and to separately examine the impact of drinking frequency and drinking quantity. Finally, survey data allow for tracking of specific patterns of risk drinking, generally defined as drinking at a level that might result in psychomotor impairment.
Because of the importance of sur vey data for estimating relationships between drinking and alcohol-related outcomes-and thus for the formula tion of low-risk drinking guidelinesthe general approaches and specific questions used to assess alcohol con sumption have received much atten tion (Alanko 1984;Armor and Polich 1982;Midanik and Harford 1994;DEBORAH A. DAWSON, PH.D., is a bio medical mathematical statistician at the National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland. Rehm 1998;Room 1990). Despite diverse national traditions regarding the measurement of alcohol con sumption, researchers have made progress toward achieving consensus on key issues guiding the selection of an optimal approach (Dawson and Room 2000), at least for Western, developed societies. This article dis cusses some of the issues that warrant consideration in the design and conduct of surveys. These issues include the choice of reference period, the types of questions asked to measure quantity and frequency of consump tion, the use of beverage-specific ver sus overall consumption questions, open-ended versus precoded responses, and definitions of drinking status. This article also describes how the data obtained in the surveys can be used to estimate alcohol consump tion. Finally, the influence of various interview modes, including the use of computerized surveys, is explored as well as other measurement considera tions, such as the confidentiality, rep resentativeness, reliability, and validi ty of the data.

Reference Period
One critical issue in survey design concerns the reference period for which consumption data are collected. This period may range from the past year to the past month, past week, or most recent drinking occasion. The choice of reference period directly affects the way in which consumption can be assessed. With short reference periods (i.e., 1 week or less) researchers can ask respondents to describe the exact number, size, and type of drinks they consumed on each day. This approach, referred to as exact recall, is thought to minimize problems with memory loss and avoids the problems inherent in trying to describe a respondent's "usual" pattern of intake.
Despite these important advantages, exact recall approaches are associated with equally significant limitations. First, the short recall period may not accurately represent the respondent's typical consumption throughout the year, particularly in populations where drinking volumes or patterns vary according to season or are influenced by various holidays. Second, the exact recall approach is not well suited to populations where many drinkers con sume alcohol on an infrequent or irreg ular basis. In these cases, an exact recall approach is likely to misclassify many infrequent drinkers as abstainers even though it may accurately estimate the volume of consumption at the popula tion level (assuming that a representa tive week is selected).
Third, a short recall period generally is inadequate for simultaneously assess ing alcohol-related problems, many of which occur rarely and can be measured with sufficient precision only over a period of at least 1 year. If the intent of a survey is to link the respondents' reports of drinking and alcohol prob lems, it is critical that the reference period for the problems not precede that for consumption (as would be the case if alcohol problems were assessed for the past year but consumption only for the past week). Inferring that alco hol plays a role in causing problems is difficult enough when one uses a com mon reference period for both con sumption and the appearance of the problems. Establishing a cause-effect relationship becomes impossible, however, when it is highly likely that the problems preceded the drinking behav ior measured. Consequently, the use of exact recall of consumption during a short reference period is most appro priate in populations where drinking is frequent and regular. In addition, this approach is more useful when the pri mary goal of a survey is to describe the volume of alcohol intake rather than to link consumption with data on prob lems measured in the same survey.
A longer reference period (i.e., 1 year) is recommended for assessing both drinking behavior and problems in countries such as the United States, where many people are light, irregular drinkers and where largescale surveys assessing both alcohol consumption and related problems permit individual-level linkage of both types of data. With such a reference period, respondents obviously cannot be asked to recall each drink they consumed during that time. Instead, researchers have developed various approaches to estimate the respon dents' usual consumption. The chal lenge with these approaches is how best to collect information that can simultaneously yield accurate esti mates of drinking frequency, volume (i.e., the amount of pure alcohol con sumed), quantity (i.e., the number of drinks per drinking day or drinking occasion), and variability, as well as the prevalence of risk drinking. Over the course of several decades of nationwide alcohol surveys conducted in the United States, two general ways of obtaining summary con sumption data have evolved-the quantity/frequency (QF) approach and the graduated frequency (GF) approach (Room 1990;Greenfield 2000), which are discussed in the fol lowing section.

The QF and GF Approaches to Measuring Alcohol Consumption
In most surveys, the QF and GF questions pertain to consumption in the past year, which is typically thought to reflect the respondent's current drinking status. However, these approaches can also be applied to other reference periods. For exam ple, in studies that focus on the etiol ogy of chronic medical conditions, the QF and GF questions can be asked so that they pertain to the peri od of heaviest drinking or to various life stages. In general, however, inves tigators have devoted less attention to measuring lifetime consumption (Lemmens et al. 1997;Russell et al. 1997;Skinner and Sheu 1982;Sobell and Sobell 1992) than to measuring current consumption.

The QF Approach
In its most basic form, the QF approach measures alcohol consumption with two simple questions that inquire about (1) the overall frequency of alcohol con sumption within the reference period, and (2) the usual number of drinks con sumed on days when the respondent drank alcohol. The variable "usual number of drinks" theoretically mea sures the most commonly consumed quantity (i.e., the mode), although past research suggests that responses actually may reflect a quantity somewhere between the mode and mean (Gruenewald et al. 1996). 1 Researchers generally do not inquire about mean consumption (which would provide a more accurate estimate of the volume consumed) because such a question would require the respondents to perform the difficult mental task of averaging what may be a highly variable distribution of quantities consumed. Moreover, information about usual consumption best represents the risks most often associated with a person's alcohol intake. For example, a person who drinks once a week and usually consumes seven drinks on that occa sion will have a higher risk of traffic crashes than a person who consumes one drink every day, even though both of them have identical volumes of alcohol intake. Consequently, infor mation about usual consumption is desirable in analyses that consider quantity and frequency of consump tion as independent risk factors.
The standard QF questions can be expanded to yield more accurate information about the respondent's drinking behavior. For example, although QF questions may assume a standard drink size that contains a fixed amount of alcohol (typically 0.5 or 0.6 ounces of pure alcohol), they can be expanded to ask about the actual sizes of the drinks consumed. (For more information on standard drinks, see the sidebar, p. 21.) Additional questions can inquire about the largest quantity consumed during the reference period or the frequency of consuming five or more (5+) drinks, which is considered an indicator of risk drinking. Finally, interviewers can ask separate series of questions about different types of beverages. (The advantages and disadvantages of beverage-specific versus overall ques tions are discussed in more detail in the following section.) One example of an expanded series of QF questions is the 1992 National Longitudinal Alcohol Epidemiologic Survey (NLAES), sponsored and con ducted by the National Institute on Alcohol Abuse and Alcoholism (NIAAA). For each beverage type, the survey asked about usual drinking fre quency and number of drinks, typical drink size, largest number of drinks consumed on one occasion, and fre quency of consuming the largest num ber of drinks (see the textbox p. 22). These beverage-specific questions were followed by a single question on the overall frequency of consuming 5+ drinks, regardless of type. Similarly, the 2001 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), being conducted by NIAAA, also included a question on the frequency of consuming 5+ drinks for each beverage type. Moreover, that survey repeats the entire series of ques tions for overall consumption of any alcoholic beverages, regardless of type.
Participants at a conference con ducted in April 2000 concluded that the briefest set of questions that could be used to measure alcohol intake adequately would consist of an expanded QF series inquiring about (1) usual quantity, (2) overall fre quency, and (3) frequency of consum ing 5+ drinks, as a measure of the prevalence of risk drinking (Dawson and Room 2000).

The GF Approach
The GF approach, which since 1979 has been used in varying forms in the National Alcohol Surveys, conducted by the Alcohol Research Group, asks respondents how often during the designated reference period they drank various quantities of standard drinks (e.g., one to two drinks, three to four drinks, and so forth). 2 Typically, the respondent is first asked the largest quantity of drinks consumed during the reference period. Then he or she is asked about the frequency of con suming all the quantity categories that include or are lower than the reported maximum (for an example of this approach, see the textbox on p. 23).
Thus, in contrast to the QF ap proach, the GF approach provides a standard set of drinking pattern mea sures-that is, the quantities of drinks for which frequencies are reported are the same for all respondents-thereby facilitating the analysis of drinking patterns, estimation of risk curves, and presentation of results. This stan dardization can be achieved only if respondents are required to report their consumption in terms of stan dard drinks rather than actual drink sizes. 3 This requirement may intro duce a source of error, however, because past research has shown that not all respondents attempt to convert their actual drinks to standard drinks and that some are incapable of doing so because they cannot accurately esti mate their actual drink sizes (Kaskutas and Graves 2000). These findings suggest that the standardization of data across respondents, which is part of the appeal of the GF approach, may be more apparent than real. The findings also underscore the need for representational aids (e.g., actual glasses and bottles or life-size photographs indicating different fill levels) to assist survey respondents in converting actual to standard drinks. Even in the QF format, representational aids are recommended to help respondents estimate actual drink sizes accurately.
The QF and GF approaches also differ in how they estimate overall drinking frequency from the data. The QF asks respondents to provide a direct estimate of the overall drinking fre quency, followed by optional questions 1 The difference between the mode and the mean is illus trated by the following example: Assume a respondent reports drinking 1 drink 100 times per year and 4 drinks 50 times per year. The mode of consumption would be one drink per occasion (the amount consumed on most occasions). The mean consumption, however, would be two drinks per occasion. 2 The evolution of the GF approach and some of its vari ants, including the cumulative frequency approach, have been discussed in detail by Greenfield (2000). 3 The GF approach could be used to ask about actual drink sizes; however, the responses would no longer be comparable across respondents without statistical manip ulation.

Standard Drinks
A standard drink is the amount of an alcoholic beverage that contains a fixed amount of pure alcohol (i.e., ethanol). Different countries have adopted a variety of standard drink sizes, ranging from a low of 8 grams (0.34 oz) of ethanol in the United Kingdom to a high of 19.75 grams (0.85 oz) of ethanol in Japan (International Center for Alcohol Policies 1998). Although the United States has no official definition of standard drink size, the two sets of drink sizes most commonly used are those volumes of various beverages that contain 0.6 oz (approximately 14 grams) and 0.5 oz (approximately 12 grams) of ethanol.
The usefulness of the standard drink concept in measur ing consumption, presenting meaningful risk curves, and developing low-risk drinking guidelines depends on all stan dard drinks containing the same amount of ethanol regardless of beverage type. Thus, in the United States (although not in all countries), a standard drink of beer contains the same amount of ethanol as does a standard drink of wine or dis tilled spirits. Different types of beverages contain different proportions of ethanol by volume. Therefore, the drink size (i.e., the actual volume of beverage) corresponding to a U.S. standard drink varies according to beverage (see table).
Although for many types of beverages (e.g., regular beer, regular wine, or distilled spirits) a standard drink closely reflects the sizes in which these beverages typically are packaged or served, this is not the case for other types of beverages. For example, one 16-ounce bottle or can of malt liquor contains approximately two standard drinks. Beverages whose container or serving sizes do not correspond to standard drinks may pose problems for drinkers, both when they try to report their level of alcohol consump tion and when they try to adhere to low-risk drinking guidelines that are stated in terms of standard drinks. on frequency of consuming 5+ drinks ple, in the QF, respondents may

Beverage-Specific versus
or the largest quantity of drinks. In report a frequency of consuming 5+

Overall Questions
contrast, the GF estimates overall drinks that exceeds their overall frequency as the sum of the quantityfrequency; in the GF, the sum of the The basic QF and GF structures lend specific frequencies. Each approach quantity-specific frequencies may themselves equally well to questions is prone to different types of error exceed the number of days in the on overall alcohol consumption or on that require reconciliation. For examreference period.
consumption of individual types of

EXAMPLE OF A QUANTITY/FREQUENCY (QF) QUESTIONNAIRE: QUESTIONS ASKED IN THE 1992 NATIONAL LONGITUDINAL ALCOHOL EPIDEMIOLOGIC SURVEY (NLAES)
Respondents were first asked the following series of questions for each type of beverage individually. These beverage-specific questions were then followed by a single question on the overall frequency of consuming five or mor (cans/bottles/glasses) of beer in a single day? e drinks on one occasion, regardless of beverage type.
• During the last 12 months, about how often did you USUALLY drink any beer?
• What was the size of the TYPICAL can, bottle, or glass of beer that you drank during the last 12 months?
• On the days when you drank beer in the last 12 months, about how many (cans/bottles/ glasses) did you USUALLY drink in a single day?
• During the last 12 months, what was the LARGEST number of (cans/bottles/glasses) of beer that you drank in a single day?
• About how often did you drink (number reported in previous question) beverages. Past studies have consistently shown that data from beverage-specific questions, when summed across bever ages, yield higher estimates of con sumption than data from a single series of questions on overall consumption (Dawson 1998;Russell et al. 1991). However, investigators cannot simply add drinking frequencies across bever ages to estimate overall drinking fre quency because respondents may con sume more than one type of beverage per day. In order to collect optimal data on both volume and pattern of drink ing, surveys should therefore include both beverage-specific questions and questions on overall consumption. Questions about overall consumption need not be asked in comparable detail to the beverage-specific questions but should at least contain questions on overall frequency of consuming any alcohol and overall frequency of con suming 5+ drinks, or a similar indicator of risk drinking (e.g., frequency of being intoxicated or feeling the effects of alcohol). When adopting a beverage-specific approach, U.S. surveys typically ask separate series of questions for at least the three basic categories of liquorbeer, wine, and distilled spirits. Many surveys add a separate series of ques tions on coolers, because respondents sometimes do not know what type of liquor their coolers contain (e.g., wine, malt, or spirits). In many sur veys the category of coolers includes all premixed drinks-that is, all drinks to which the manufacturer has added some form of alcohol. If a sur vey contains questions about coolers, these typically precede questions on beer, wine, and spirits. That way, respondents can be instructed not to repeat any information on wine cool ers and premixed cocktails in response to the questions regarding consump tion of wine and distilled spirits, respectively. If space permits, investi gators also may include separate series of questions on malt liquor and forti fied wine because these beverages have higher alcohol contents than regular beer and wine, respectively, and often are consumed in different size con tainers or glasses (for more informa tion, see the sidebar, "Standard Drinks").
Whenever respondents are asked both beverage-specific and overall questions, the responses may be inter nally inconsistent. For example, respondents may report an overall fre quency of drinking that is lower than the reported frequency of drinking for a specific beverage type. These types of inconsistencies typically are resolved in data editing. 4 Computerassisted interviews also may include specific questions (i.e., probes) that allow the interviewer to resolve such apparent discrepancies during the interview. 5 Inconsistencies may also be reduced if researchers ask the beveragespecific questions before the questions on overall consumption, thereby help ing respondents to focus on the full extent of their alcohol consumption. In addition, this approach may allow interviewers to shorten the interview by skipping the overall questions for respondents who reported drinking only one type of beverage. (In this case, one must be willing to assume, however, that the respondent did not drink any types of beverages other than those mentioned in the interview.) The approach of asking the beverage-specific questions first may also have some disadvantages, howev er. For example, it may increase the possibility that respondents will mis interpret the questions on overall consumption as referring to times when they consumed more than one type of beverage. Moreover, respon dents who drank only one type of beverage may find the overall ques tions repetitive or confusing.

Open-Ended versus Precoded Response Categories
Alcohol surveys typically provide the respondents with precoded response categories representing frequency of drinking rather than asking for the actual number of drinking days. For example, research has shown that respondents find it easier and less embarrassing to report a frequency of "once a week" than of "52 times," at least when reporting sensitive infor mation, such as frequency of heavy drinking in the past year (Ivis et al. 1997). The order of these response categories can influence the accuracy of the respondent's answers. Ordering response categories so that the highest frequencies are at the top of the list (i.e., "asking down") helps to make higher frequencies seem more normal and less embarrassing to the respon dent (Dawson and Room 2000

EXAMPLE OF A GRADUATED FREQUENCY (GF) QUESTIONNAIRE
For the GF approach, respondents are first asked about the largest number of drinks they have consumed in one day during the year preceding the interview. They are then asked how often during that period they consumed various quantities of standard drinks, starting with the category that includes the reported maximum. (This example assumes that the largest reported number of drinks consumed in one day is 12.) • During the last 12 months, what is the largest number of drinks you had on any single day?
• During the last 12 months, how often did you hav kind of alcoholic bev e 12 or more drinks of any kind of alcoholic beverage in a single day-that is, any combination of cans of beer, glasses of wine, or drinks containing liquor of any kind?
• During the last 12 months, how often did you have at least 8 but less than 12 drinks of any kind of alcoholic beverage in a single day?
• During the last 12 months, how often did you have 5, 6, or 7 drinks of any kind of alcoholic beverage in a single day?
• During the last 12 months, how often did you have 3 or 4 drinks of any kind of alcoholic bev erage in a single day?
erage in a single day?
• During the last 12 months, how often did you have 1 or 2 drinks of any • Once a month • 7 to 11 times a year categories rather than in 1 of 365 pos sible categories. If investigators want to • 3 to 6 times a year cover a wider range of responses for • 1 or 2 times a year analytic purposes, an alternative approach that increases the number of • Never.
response options is to ask respondents an open-ended question on how often In personal interviews, respondents they drank and vary the time period, frequently are given a response card with the response coded into the fol and asked to provide just the letter or lowing format: number of the category. Using letters [ ] Week rather than numbers to identify the _____________ per [ ] Month categories helps researchers avoid con-Number of times [ ] Year fusion as to whether a verbal response of, for example, "one" means "one Although this format, which has been time" or the category labeled 1.
used repeatedly in the National A possible disadvantage of precoded Health Interview Survey, gives respon response categories is that they limit dents alternatives for reporting high the number of possible responses, espe-frequencies of consumption, it does cially in the upper ranges of frequen-not offer them the option of simply cies. For example, a response of "nearly reporting the letter or number corre every day" in the categories listed above sponding to a response category. could actually mean anything from Furthermore, this format requires 209 times to 364 times. Overall, the careful training of the interviewers so responses with these precoded ques-they know what to record or how to tions fall into 1 of only 10 nonzero probe when the response is vague (e.g., "nearly every day") or includes a range for the number of times (e.g., "2 or 3 times a month"). Surveys that assess actual drink sizes rather than standard drinks also commonly use precoded response cat egories. The categories provided in such surveys should reflect the con tainer sizes in which the beverage is commonly sold and consumed (e.g., the available sizes of cans and bottles of beer). Alternatively, the categories should correspond to the fill lines shown on any representational aids provided to help the respondents assess how many ounces they con sume in a typical glass.
Questions on the usual and largest quantity of alcohol consumed often are asked in an open-ended format. However, these questions also may be asked using precoded response cate gories similar to those used in the GF approach (e.g., 1-2 drinks, 3-4 drinks, 5-7 drinks, 8-11 drinks, and 12 or more drinks).

Determination of Drinking have a great impact on how the U.S. Status
adult population is classified by drinking status (see the table). The Most surveys aimed at determining 1992 NLAES defined these categories past-year consumption begin with a as follows: short series of questions intended to ascertain the respondent's drinking • Lifetime abstainers are people who status and to avoid asking nondrinkers have never consumed 12 or more a large number of inapplicable ques-(12+) alcoholic drinks in any one tions. Based on these introductory year. questions, respondents generally are classified into one of three categories • Former drinkers are people who have of drinking status-lifetime abstainer, consumed 12+ drinks in at least one former drinker, and current (i.e., year but not in the past year. past-year) drinker. Distinguishing lifetime abstainers from former • Current drinkers are people who drinkers is particularly important in consumed 12+ drinks in the past epidemiological research, because any year. health benefits of light-to-moderate drinking (e.g., reductions in coronary The 1988 National Health Interheart disease [Rimm et al. 1996]) view also defined categories based on may be exaggerated when former consumption of at least 12 drinks in drinkers-who may have been heavy various time periods, but it distin drinkers who stopped drinking guished lifetime abstainers (who drank because of adverse health effects-are fewer than 12 drinks in their lives) included in the category of abstainers from lifetime infrequent drinkers (who (Shaper 1995).
drank 12+ drinks in their lives but The specific definitions of abstainnot in any one year). The National ers, former drinkers, and current Alcohol Surveys as well as the 2001 drinkers, however, can vary across NESARC used the broadest possible surveys, and these definitions can definition of drinkers and therefore

Lifetime infrequent
identified the largest proportion of current drinkers by using the follow ing categories: • Lifetime abstainers are people who have never had an alcoholic drink.
• Former drinkers are all people who have had a drink at some time in their lives but not in the year preceding the interview.
• Current drinkers are all people who have had at least one drink in the past year.
In the NESARC, these definitions were supplemented by questions on drinking 12+ drinks in the past year, thereby providing maximum flexibili ty for comparing the data with all earlier studies.

Estimating Alcohol Consumption
The questions and definitions described in the previous sections serve as the basis for determining respondents' overall alcohol consumption. To this end, researchers must create analytic measures that describe drinking pattern and volume. At a recent confer ence devoted to measuring alcohol consumption, participants recom mended the following items for pre sentation and analysis of consumption data (Dawson and Room 2000): • Drinking status The conference participants recommended frequency of consuming 5+ drinks as an indicator of risk drinking, despite its acknowledged limitations. For example, this measure does not account for the extent to which factors such as total body water, tolerance, and time between drinks might affect resulting blood alcohol levels.
Instead of volume of ethanol intake, researchers can report frequency and usual or average quantity of alcohol intake (Greenfield 1986). Moreover, the frequency of drinking 5+ drinks may be replaced with the statistical concept of variance around a mean intake per day or by an index of risk drinking that varies with volume (Greenfield 1986). Measures that involve multiple categories rather than a continuous measure (i.e., categorical measures), such as the Volume-Variability Index-which includes categories such as low volume plus low maximum consumption, low volume plus high maximum consumption, and so on (see Cahalan et al. 1969)-have been cited for their descriptive value. However, measures based on large num bers of categories pose problems of statistical inefficiency in multivariate models predicting alcohol-related outcomes as a function of consump tion, especially when looking at the interaction of consumption with other measures.
The frequency of consuming 5+ drinks can be determined relatively easily. In the expanded QF approach, this question is asked directly. When using the GF approach, investigators must add the frequencies of all cate gories of 5 or more drinks (e.g., fre quencies of drinking 5-7, 8-11, and 12+ drinks). If the frequency cate gories include a range of frequencies, the midpoint of these values is used (e.g., "2 to 3 times a month" is con verted to 2.5 times per month or 30 times per year). When beveragespecific questions are included in a survey, the frequency of risk drinking must be based on overall questions that ask about consumption of any type of alcohol. As mentioned earlier, one cannot simply add beveragespecific frequencies because a drinker may consume 5+ drinks of more than one type of beverage on a given day (e.g., six glasses of beer plus six shots of distilled spirits). Finally, the preva lence of risk drinking is defined as the proportion of respondents (or current drinkers) who consume 5+ drinks with some specified frequency (e.g., ever in the past year, at least once a month, or at least once a week).
The calculations for estimating the volume of ethanol intake are more complex and differ substantially between the QF and GF approaches (for examples of all calculations, see the sidebar on p. 26). In the most basic form of the QF, when only usual quantity and overall frequency are asked, annual volume of ethanol intake is calculated by multiplying usual quantity times overall frequency of drinking (in days per year) times the assumed ethanol content of a standard drink (e.g., 0.6 ounces). When actual drink size is asked, the assumed ethanol content is replaced by the actual ethanol content. This quantity is calculated by multiplying the typical size of drink (i.e., ounces of beverage) times the ethanol conversion factor (i.e., the percentage ethanol by volume) of the beverage (for more information, see the sidebar, "Standard Drinks"). If beveragespecific questions are asked, overall ethanol consumption is the sum of the results for all types of beverages.
When questions on largest quantity are added, annual ethanol intake has two components: • The usual quantity times the fre quency of drinking that quantity (i.e., the overall frequency of drink ing minus the frequency of drinking the largest quantity) • The largest quantity times the fre quency of drinking the largest quantity.
The sum of these two components is then multiplied by the standard or actual drink size, as described above, and, if applicable, summed across beverages. For people whose largest quantity is five drinks or fewer, annual intake is calculated as described above, even when the frequency of drinking 5+ drinks is also assessed. However, the annual ethanol intake of respondents whose largest quantity of consump tion is 6+ drinks is made up of three components when based on this addi tional information: • The usual quantity times the fre quency of drinking that quantity (i.e., the overall frequency minus the frequency of drinking 5+ drinks) • Five drinks times the frequency of drinking 5+ but less than the largest quantity of drinks (i.e., the fre quency of drinking 5+ drinks minus the frequency of drinking the largest quantity) 7 • The largest quantity times the fre quency of drinking the largest quantity.
Again, the sum of these three products is multiplied by the standard or actu al drink size, as described previously, and summed across beverages. Using the GF approach, researchers can estimate the annual ethanol intake quite simply. Because this approach assumes a standard drink size, volume is simply the product of the frequency per year times the midpoint of the quantity range (e.g., six drinks for the category of 5-7), summed across all quantity ranges and then multiplied by the ethanol content of the standard drink. As with the QF, beverage-specific values are summed across beverages to yield overall consumption.
Regardless of whether the GF or QF approach is used, the average daily ethanol intake is calculated by dividing the annual volume by 365. The average ethanol intake per drink ing day is calculated by dividing the annual volume by the overall number of drinking days per year. 7 One can also use the midpoint of the implied range instead of a quantity of five drinks. For example, for a person whose largest quantity was eight drinks, this compo nent would reflect the volume consumed on days when drinking five to seven drinks, and the midpoint of that range (i.e., six drinks) might be used instead of the more conservative value of five drinks.

Expanded QF Approach, Actual Drink Size
Overall frequency of drinking: 4 times a week = 208 days Usual quantity of drinks: 1 Largest quantity of drinks: 6 Frequency of consuming largest quantity: once a month = 12 days Frequency of consuming 5+ drinks: once a month = 12 days Standard drink size = 0.6 oz ethanol Annual volume = [(208 -12 days)(1 drink) + (12 days)(6 drinks) + (12 -12 days)(5+ drinks)] (0.6 oz) = 160.8 oz ethanol (If Joe also drinks other types of alcoholic bever ages, they would be assessed separately, and this result would be summed with the ethanol intake for those other types of beverages to yield the overall volume of ethanol intake.)

Graduated Frequency (GF) Approach, Standard Drink Size
Largest quantity of drinks consumed = 6 Frequency of drinking 5-7 drinks: once a month = 12 days Frequency of drinking 3-4 drinks: once a week = 52 days Frequency of drinking 1-2 drinks: three times a week = 156 days Standard drink size = 0.6 oz ethanol Annual volume = [(12)(6) + (52)(3.5) + (156)(1.5)] (0.6 oz) = 292.8 oz ethanol Thus, using the GF approach, Joe's annual alcohol consumption would be calculated to be more than twice as high as the amount calculated using the basic QF approach. The basic QF approach would seriously underestimate Joe's annual alcohol consumption. On the other hand, the GF approach in this example would somewhat overestimate his consumption because, although Joe would be at the lower end of both the frequency categories of 3-4 drinks and 1-2 drinks, the median value of each category is used for the calculations.

-Deborah A. Dawson
Calculating Annual Volume of Intake of Pure Alcohol (Ethanol) As described in the main article, researchers conducting surveys can use several approaches to determine the amount of alcohol the survey respondents have consumed during the reference period (e.g., the past year). These approaches range from questions about the usual quantity and frequency of alcohol consumption to more detailed questions regarding the frequency with which various predetermined quantities of alcohol were consumed. The choice of questions can strongly influence the accuracy of the results, as illustrated by the following example. Imagine a fictitious person, Joe Smith, whose annual consumption of pure alcohol is to be determined. Let's assume that Joe drinks only regular beer, typically in 12-ounce cans or bottles. Approximately three nights a week, Joe has one can of beer after dinner. On Saturdays, however, he typically consumes about three beers. And once a month, Joe gets together with some buddies to play cards, and on those nights he usually has about six beers.
Based on this information, Joe's annual consumption of pure alcohol can be compared using several mea surement approaches, as follows:

Mode of Interview
Although most of the alcohol surveys in the United States to date have been conducted as personal interviews, telephone interviews are becoming increasingly common. Telephone interviews have several advantages. They typically are less expensive to conduct because they reduce the costs associated with failed attempts to find potential respon dents at home. Telephone interviews may also reduce the discomfort of respondents who are asked to describe sensitive behaviors. At the same time, telephone interviews pose several problems with respect to mea suring alcohol consumption. Most important, telephone interviews do not offer a guaranteed way to provide respondents with visual aids, such as flashcards containing response cate gories or representations of different glass sizes and fill levels. Although such materials could be mailed in advance to potential respondents, this step would greatly increase costs without ensuring that the materials would be received and retained until the time of the interview. Consequently, telephone interviews typically use questions based on standard drink sizes that can be explained verbally and often restrict both the number and wording of response categories to permit their being read aloud as a part of the question. To date, researchers have found only small and inconsis tent differences in reports of con sumption resulting from the mode of interviewing (see the discussion in Rehm 1998).
Both personal and telephone interviews may be computerized. In computer-assisted interviews, interviewers read the survey questions from a screen, and the computer program automatically skips the interviewer past inapplicable questions and supplies the appropriate wording for questions. This technology greatly eases the administration of survey instruments with complex skip patterns, thus mini mizing interviewer error, and it may substantially reduce the burden placed on the respondent by large numbers of questions. For example, with respon dents who report three drinks as their largest quantity of consumption, the computer program can have the interviewer skip questions pertaining to the frequency of consuming 5+ drinks. Similarly, for respondents who report one drink as both their usual and largest quantity of consumption, the interviewer can skip the question that asks about the frequency of drinking the largest quantity. If a respondent reports a typical drink size of a 5-ounce glass of wine, computer programs can insert this information into the word ing of subsequent questions (e.g., "During the last 12 months, what was the largest number of 5-ounce glasses of wine that you drank in a single day?"). These features improve both the internal consistency and overall quality of the alcohol consumption data, both of which are further enhanced by the option of using builtin probes to reconcile internally incon sistent responses.
Computerized interviews also allow the interviewers to have respondents self-administer sensitive questions. In these cases, the interviewer instructs the respondent to enter his or her responses directly onto the computer or the telephone keypad. Although literacy problems may limit the use of this option in personal interviews where the questions are printed on the computer screen, this problem can be overcome by having both the ques tions and response categories read aloud on a recording that accompa nies the computerized instrument.

Other Measurement Considerations
Beyond issues specific to measuring alcohol consumption, alcohol epide miology shares concerns that affect all types of survey research. These include respondent burden; confidentiality; and the representativeness, reliability, and validity of the data collected.

Respondent Burden
The burden imposed on the respon dents by the survey is a function of both the time required to participate in an interview and any mental or emotional demands associated with the type of information respondents are asked to recall. Researchers can minimize this burden in many ways, including the following: • By excluding questions not clearly linked to specific analytic aims • By making full use of skip patterns to ensure that respondents are not asked inapplicable or unnecessary questions • By allowing respondents to report potentially embarrassing informa tion in a face-saving manner, such as by giving the letter associated with a response category • By grouping questions to avoid jumping back and forth between different time reference periods • By providing cognitive cues to assist memory as well as visual aids to assist with difficult tasks, such as estimating drink sizes • By asking questions in a way that minimizes the need to average dissim ilar quantities of intake (e.g., by ask ing usual rather than average quan tity, or by asking separate series of questions for weekday and weekend drinking in populations where most drinking takes place on weekends).

Confidentiality
All respondents should be assured of the confidentiality of their responses before being asked to divulge personal data. In fact, surveys sponsored by the Federal Government ensure this confi dentiality by law. Some of the ways in which confidentiality is maintained include: • Keeping personal identifiers, such as names or Social Security numbers, separate from public use data • Removing small-area geographic identifiers (e.g., the name of the city or county) from public use data • Combining all values above a cer tain level (i.e., top-coding) for highly skewed items (e.g., personal income) in such a manner that the uppermost value is an open-ended category sufficiently large to pre clude identification of any individ ual within it (e.g., an income cate gory of $100,000 or more).

Representativeness
The representativeness of survey data largely depends on the response rate and response error. A low response rate (i.e., a high rate of refusals to par ticipate in a survey) generally reflects either unwillingness to take the time to be interviewed or concerns about privacy. Consequently, the steps listed above for reducing respondent burden and ensuring confidentiality also serve to increase the survey response rate and, by extension, the representative ness of the sample. The term "response error" refers to the fact that some respondents provide incorrect answers to survey ques tions. Recall problems and intentional misreporting contribute to this prob lem. Response errors can be reduced through some of the techniques men tioned previously for reducing respon dent burden, notably those techniques that aim to minimize respondent confusion and embarrassment.

Reliability and Validity
Assessing the reliability and validity of responses is an important compo nent of any type of survey research. Reliability is defined as the consistency of the responses if a respondent is surveyed more than one time. The reliability of alcohol consumption measures is best assessed using a test-retest design, in which investiga tors reinterview respondents shortly after the original interview and then compare the two sets of responses. The reinterviews should be conducted by different interviewers who do not know the original responses, and the interval between the two interviewstypically in the range of 2 to 6 weeksshould not be so long as to invalidate the comparison. 8 Statistical techniques for determining test-retest reliability are available for both dichotomous measures (i.e., measures for which only a "yes" or "no" response is possi ble, such as whether the respondent ever consumed alcohol) and for con tinuous measures (i.e., measures for which numerous responses are possi ble, such as the maximum number of drinks) (Fleiss 1981). Each of these techniques corrects for the degree of agreement between the original and reinterview responses that would be expected to occur by chance alone.
Validity is defined as the extent to which a person's (or a group of peo ple's) responses in a survey approx imate the actual consumption levels. In the United States, the validity of alcohol consumption data is most often assessed in terms of coveragethat is, the extent to which alcohol consumption as determined based on survey responses accounts for all alco hol sold. Although higher coverage rates tend to be equated with better validity, it is worth noting that they also can result from errors of overreporting, such as when respondents report the same consumption in mul tiple categories (e.g., both as wine and as coolers). It also should be noted that sales data themselves may be incomplete because they fail to account for alcohol purchased in other countries, made and sold ille gally, or produced at home.
Coverage rates for U.S. surveys tend to be quite low, usually account ing for no more than 40 to 60 percent of alcohol sales (Midanik 1982;Pernanen 1974;Rehm 1998). However, it may be unrealistic to expect data from household surveys to account for all alcohol sold in the United States (Rehm 1998) because those surveys by definition exclude some subpopulations thought to have high rates of alcohol consumption, such as the homeless, people living in institutions, and members of the armed forces. Some household sur veys also exclude people living in group quarters, which means that the alcohol consumption of students liv ing in dormitories and fraternities or sororities is not measured. Restrictions on the age of respondents (e.g., adults ages 18 and over) may further contribute to the problem of incomplete assessment by failing to capture underage drinking. Beyond these caveats, however, it is clear that sur veys to date fall short of capturing all alcohol consumption. The growing emphasis on questions that go beyond usual drinking patterns to assess the quantity and frequency of atypical heavy drinking occasions represents the best promise for improving coverage.

Conclusions
This article has described the meth ods currently used in alcohol surveys in the United States. Similar or iden tical methods have been endorsed by most Western, developed countries. In contrast, serious challenges remain in adapting measurement techniques to the drinking patterns of other soci-8 An advantage of questions based on the past-year refer ence period is that they are fairly insensitive to any real changes in drinking behavior that may have taken place between the two interview dates. That is, any such changes should have little effect in terms of producing inconsistent responses.
eties, especially tribal cultures where drinking may be a communal activity delineated in terms of time rather than quantity. Even in Western soci eties, there is some doubt whether current measurement techniques are equally suitable for all population subgroups. For example, it is unclear whether different measures of risk drinking should be used for men and women to reflect gender differences in average total body water. In addi tion, researchers still need to determine how well existing measurement approaches capture atypical light drink ing among subgroups whose predominant drinking pattern is one of infrequent heavy drinking. Other areas of needed research include a comprehensive comparison of data obtained using the QF and GF ap proaches with data obtained through diary/daily recall approaches, both in terms of volume estimates and in terms of accuracy in capturing overall drinking frequency and frequency of risk drinking. Finally, researchers must investigate whether the use of arith metic midpoints for quantity and fre quency ranges is supported by data on the underlying distribution of those variables. These are some of the important issues that must be addressed in the future to continue improving the measurement of alcohol consumption. ■